Blue Line or Blueline may refer to:
Transportation
Asia
China
- Line 2 (Beijing Subway), Beijing, China
- Island line (MTR), Hong Kong, China
India
- Blue Line (Namma Metro), Bengaluru, India
- Blue Line (Chennai Metro), Chennai, India
- Blue Line (Delhi Metro), Delhi, India
- Blue Line (Hyderabad Metro), Hyderabad, India
- Blue Line (Kolkata Metro), Kolkata, India
- Blue Line (Lucknow Metro), Lucknow, India
- Blue Line (Mumbai Metro), Mumbai, India
South Korea
- Busan Metro Line 4, Busan, South Korea
- Seoul Subway Line 1, Dark Blue Line, Seoul, South Korea
- Seoul Subway Line 4, Light Blue Line, Seoul, South Korea
Taiwan
- Blue line (Taichung MRT), Taichung, Taiwan
- Bannan line, Taipei, Taiwan
Others
- Blue Line (Bangkok), Bangkok, Thailand
- Blue Line (Dubai Metro), Dubai
- Cikarang Line of KRL Commuterline, Jakarta, Indonesia
- Manila Light Rail Transit System Line 2, Manila, Philippines
- Line 1 (Riyadh Metro), Blue Line, Riyadh, Saudi Arabia
- Downtown Line, Singapore
- Blue Line (Yokohama), also called Lines 1 & 3, Yokohama, Japan
- Blue Line (Jerusalem Light Rail)
Europe
- Blue Line (airline), based in France
- Blue Line (Lisbon Metro), Portugal
- Blue Line (Stockholm Metro), Sweden
- Blue Line International, a former ferry service in the Adriatic Sea
- Barcelona Metro line 5, often called "Línia Blava" (Blue Line), Barcelona, Spain
- Barcelona Metro line 6, Barcelona, Spain
- Paris Metro Line 2, Paris, France
- Piccadilly line, London, England
- Sheffield Supertram Blue Line, United Kingdom
- Tyne and Wear Metro of Newcastle upon Tyne, UK (Former line)
- Victoria line, London, England
North America
New York City
- The Harlem Line of the Metro-North Railroad
- The Hoboken–33rd Street route of the PATH Train
- Any of the New York City Subway services that use the IND Eighth Avenue Line and its branches:
- A Eighth Avenue Express
- C Eighth Avenue Local
- E Eighth Avenue Local
- The former K Eighth Avenue Local
- The Rockaway Park Shuttle, which formerly contained a blue route bullet
- The Port Jefferson Branch of the Long Island Rail Road
- The former JFK Express of the New York City Subway
- The future T Second Avenue Local of the New York City Subway
- The West Hempstead Branch of the Long Island Rail Road
- The Staten Island Railway
Other
- ARTx Blue Line, formerly Rapid Ride, Albuquerque, New Mexico
- Blue Line (MARTA), Atlanta, Georgia
- Blue Line (CapMetro), Austin, Texas
- Blue Line (MBTA), Boston, Massachusetts
- Blue Line (Calgary), Calgary, Alberta, Canada
- Lynx Blue Line, Charlotte, North Carolina
- Blue Line (CTA), Chicago, Illinois
- Blue Line (RTA Rapid Transit) (light rail), Cleveland, Ohio
- Blue Line (DART), Dallas, Texas
- Trinity Railway Express, Dallas, Texas
- H Line (RTD), Denver, Colorado
- A Line (Los Angeles Metro), Los Angeles County, California
- Blue Line (Mexico City Metro), Mexico
- Blue Line (Mexico City Metrobús), Mexico
- Metro Blue Line (Minnesota), Minneapolis, Minnesota
- Blue Line (Montreal Metro), Montreal, Quebec
- Atlantic City Line, a commuter rail line New Jersey
- Grove Street – Newark Penn, a light rail line in Newark, New Jersey
- North Jersey Coast Line, a commuter rail line New Jersey
- Blue Line (Pittsburgh), Pittsburgh, Pennsylvania
- Market–Frankford Line, Philadelphia, Pennsylvania
- Blue Line (SacRT), Sacramento, California
- Blue Line (San Diego Trolley), San Diego, California
- Blue Line (BART), San Francisco Bay Area, California
- N Judah, a Muni Metro light rail line in San Francisco, California
- Line 3 Scarborough, Toronto, Canada
- Viva Blue, York Region, Ontario
- MAX Blue Line, Portland, Oregon
- Blue Line (St. Louis MetroLink), St. Louis, Missouri
- Blue Line (Sound Transit), a proposed extension in Seattle, Washington
- Swift Blue Line, Snohomish County, Washington
- Blue Line (TRAX), a light rail line in the Salt Lake City, Utah area
- Blue Line (Washington Metro), Washington, DC
- Tomorrowland Transit Authority PeopleMover, Walt Disney World, Florida
- Line 4 (O-Train), the Airport Link of Ottawa's O-Train (Line 4)
South America
- Line 1 (São Paulo Metro), São Paulo, Brazil
Africa
- Blue Line (Lagos Transit), Lagos, Nigeria
- Blue Line, part of the Abuja Light Rail Network in Abuja Nigeria
Other
- Blue Line (album), by Yae
- Blue line (ice hockey), the line between center ice and each team's zone
- Blue Line (withdrawal line), the UN drawn demarcation line dividing Lebanon from Israel and the Golan Heights
- Blue Line (New York State), delineates the Adirondack and Catskill parks of New York's Forest Preserve
- BlueLine Grid, a mobile communications platform that connects civil service employees
- Blueline, a 2019 EP by twlv
- The "blue line", mark on an airspeed indicator for a multi-engine aircraft
- The blue-line printing process for copying using the diazo chemical process, also known as whiteprint
- The Blueline Blaster, nickname of Hy Buller (1926–1968), All Star NHL ice hockey player
- Blue line, a diagram in method ringing which shows the structure of a method
- Blue-line stream, year-round streams that are typically denoted on maps with solid blue lines
- "Blue Lines", a song by the American band Bright from the album Full Negative (or) Breaks